<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>reduce</title>
    <script type="text/javascript">

        let arr = ['1', '20', '-5', '3'];

        arr = arr.map(ele=>parseInt(ele));

        let result = arr.reduce((a,b)=>a*b,-1);

        console.log(result);


    </script>
</head>
<body>

</body>
</html>